The present invention relates to a master cylinder. More particularly, it relates to a master cylinder that is suited for an automobile on which a working fluid is returned from a wheel cylinder to a reservoir through a working fluid passage for the master cylinder when brake control is released on an automobile provided with a unit in which a working fluid for the wheel cylinder is pressurized by pumping-up to carry out brake control (traction control unit, automobile stability control unit, etc.), and that decreases the noneffective piston stroke of the master cylinder at the time of ordinary operation.
FIG. 20 is a sectional view showing one example of a conventional master cylinder, which has been disclosed in Japanese Patent Application Provisional Publication No. 10-53120 (No. 53120/1998). This master cylinder 1 has a piston 3 fitted slidably in a cylinder bore 2a formed in a cylinder body 2, and is provided with a pressure delivering chamber 4 defined by the piston 3 and a supply passage 5. The piston 3 is fitted with a valve mechanism 6 and a floating throttle valve mechanism 7 on the extension of the axial line. The valve mechanism 6 opens an axial hole 12 with a flange 10 integral with a rod 9 being separated from an annular member 11 in response to the retreat of the piston 3 to the return position effected by a return spring 8 installed in the pressure delivering chamber 4, and closes the axial hole 12 with the flange 10 coming into contact with the annular member 11 in response to the advance of the piston from the return position.
Also, the floating throttle valve mechanism 7, which is provided with a floating member 13 having a throttle hole 13a, moves the floating member 13 to a throttling position at which a throttle effect is given to the flow of a working fluid when the working fluid flows toward a reservoir, not shown, and moves the floating member 13 to a non-throttling position at which no throttle effect is given to the flow of the working fluid when the working fluid flows from the reservoir toward the pressure delivering chamber 4 through the axial hole 12.
The piston 3 begins to operate in the state in which the valve mechanism 6 is open, and advances in the left-hand direction in the figure, whereby the valve mechanism 6 is closed. Therefore, the communication between the pressure delivering chamber 4 and the supply passage 5 is cut off. Subsequently, by moving the piston 3 further in the left-hand direction, a pressure is delivered in the pressure delivering chamber 4, and the working fluid is discharged through an output port 14. During the time elapsing from when the piston 3 begins to advance to when the valve mechanism 6 closes, the working fluid in the pressure delivering chamber 4 is made to flow by the advance of the piston 3 so as to go into the supply passage 5 through the floating throttle valve mechanism 7 and the valve mechanism 6. At this time, by the flow of the working fluid, the floating member 13 of the floating throttle valve mechanism 7 closes a communication hole 15a in a case 15. Thereby, the working fluid in the pressure delivering chamber 4 is made to flow into the supply passage 5 through the throttle hole 13a in the floating member 13. The quantity of working fluid flowing from the pressure delivering chamber 4 into the supply passage 5 decreases as compared with the case where the flow of working fluid from the pressure delivering chamber 4 to the supply passage 5 is not throttled.
However, for a master cylinder used for an automobile provided with a traction control unit and an automobile stability control unit, in the case where there is provided a throttle valve mechanism (for example, an orifice) for decreasing the quantity of working fluid flowing from the pressure delivering chamber 4 to the reservoir at the time of operation start (at the time of piston advance), there arises a problem in that a delay in returning fluid to the reservoir or a delay in lowering the fluid pressure in the pressure delivering chamber 4 is encountered because of the interposition of the throttle valve mechanism in the passage when the working fluid is returned from the wheel cylinder to the reservoir via a make-up liquid passage of the master cylinder at the time when the traction control unit and the automobile stability control unit are released.
Also, in the case where the throttle valve mechanism is provided in a portion in which the master cylinder and the reservoir are connected to each other, when liquid is returned from the pressure delivering chamber to the reservoir, there arises a problem in that a high pressure is delivered in a portion in which the master cylinder and the reservoir are connected to each other, and a force acts in the direction toward the reservoir tank, so that the cost is increased by the increased strength of a tank holding construction.
For these reasons, there has been demanded a master cylinder having a construction in which the throttle valve mechanism can respond quickly to an increase/decrease in the quantity of the returned working fluid (that is, a change in pressure) at the time when the traction control unit and the automobile stability control unit are released.
The present invention has been made in view of the above situation, and accordingly an object thereof is to provide a master cylinder for an automobile provided with a traction control unit and an automobile stability control unit, which has a simple and small valve construction which can decrease the quantity of working fluid flowing to a reservoir at the time of operation start of master cylinder, and can respond to the fluctuations in fluid pressure quickly when the traction control unit and the automobile stability control unit are released, and which is capable of decreasing the noneffective piston stroke.
To achieve the above object, the present invention is configured as follows in a master cylinder in which a piston is disposed slidably in a cylinder bore formed in a cylinder body; a pressure delivering chamber is defined by the piston and the cylinder body; a fluid passage, which connects the pressure delivering chamber to a reservoir, for resupply the working fluid to the pressure delivering chamber is provided; and a working fluid whose pressure is increased in the pressure delivering chamber is discharged through an output port at the operation time of the piston.
A throttle valve mechanism having a throttle function of throttling the flow of working fluid from the pressure delivering chamber to the reservoir at the operation time of the piston, a valve function of allowing the working fluid to flow from the reservoir to the pressure delivering chamber by opening the valve at the return time of the piston, and a relief valve function of allowing the working fluid to flow from the pressure delivering chamber to the reservoir is disposed in the fluid passage.
The throttle valve mechanism has a valve seat provided at the tip end of a connector of the reservoir with the cylinder body, and a floating valve disc formed of an elastic material formed with a throttle hole and a plurality of slits in a substantially central portion thereof, which has a valve seat face which is seated against the valve seat.
Alternatively, the throttle valve mechanism has a thin-sheet or thin-film valve sheet formed of an elastic material, a rib formed at the tip end of the connector of the reservoir with the cylinder body, with which the valve sheet comes into contact from the pressure delivering chamber side, and a fixing portion for fixing the valve sheet, and in the normal state in which the valve sheet is not deformed, a slit for throttling is formed between the outer peripheral edge of the valve sheet and the inner peripheral face of tip end of the connector of the reservoir.
Alternatively, the throttle valve mechanism has two large-diameter and small-diameter thin-sheet or thin film valve sheets, each formed of an elastic material, a rib formed at the tip end of the connector of the reservoir with the cylinder body, with which the large-diameter valve sheet comes into contact from the pressure delivering chamber side with the small-diameter valve sheet being interposed between the rib and the large-diameter valve sheet, and a fixing portion for fixing both of the valve sheets in a substantially central portion of the rib; a through hole is formed in a portion in which the small-diameter valve sheet laps over the large-diameter valve sheet; and in the normal state in which the large-diameter valve sheet is not deformed, a slit for throttling is formed between the outer peripheral edge of the large-diameter valve sheet and the inner peripheral face of tip end of the connector of the reservoir.
Alternatively, the throttle valve mechanism has a floating valve disc formed of an elastic material formed with a throttle hole, and a sheet face formed on the inner peripheral face of a valve chest, which is a passage between the tip end of the connector of the reservoir with the cylinder body and the cylinder body side of the connector, so as to be inclined with respect to the valve axis, the connector having a through groove in the tip end thereof and being formed with a valve seat with which the floating valve disc floating in the valve axis direction comes into contact, so that when the floating valve disc moves toward the reservoir, the valve is closed, and when the floating valve disc moves toward the cylinder body, the valve is opened.
Since the present invention is configured as described above, when the working fluid flows from the pressure delivering chamber to the reservoir at the time of operation start of the piston of master cylinder, the working fluid flows through the throttle mechanism only, so that the quantity of working fluid flowing to the reservoir is decreased.
Inversely, when the working fluid flows from the reservoir to the pressure delivering chamber at the return time of the piston, including the operation time of the traction control unit (or the automobile stability control unit) of automobile, a check valve mechanism is opened by the flow of the working fluid, so that the working fluid flows mainly through the check valve mechanism.
Also, when a large quantity of high-pressure working fluid flows from the pressure delivering chamber to the reservoir at the release time of the traction control unit (or the automobile stability control unit) of automobile, a relief valve mechanism is opened by the great flow of working fluid, so that the working fluid flows through the relief valve mechanism. Therefore, the throttle valve mechanism responds quickly to the fluctuations in fluid pressure. At the same time, the above-described mechanism can decrease the noneffective piston stroke of master cylinder.